Before leaving the beach, I would like to mention another common phenomenon. I am not a diver, and in fact only experienced the adventure once. During that dive I was amazed at the sharp, vivid, intense colors of the choral and other objects beneath the sea. However, when I looked at an object above the surface in stark sunlight, I was equally surprised to find that the sharp vivid colors where not there. Instead only dim, faint colors. According to my definition above, this would imply that we are in a visual illusionary state as we marvel at the undersea panorama.
Now to subjective illusions. These are the kind a camera will not record. They are totally dependent on your “mind” or cerebral processes in your brain or visual system. As an interesting example, I consider a type of illusion called “The Mach Strip” using A. D. Smiths description from “The Problem of Perception.” “Take a sheet of white paper, fold it lengthwise down the middle, and place it on a flat surface so that, as you look down on it, it looks like a roof extending away from you. Position it so that more light falls on one side of the “roof” than the other. Close one eye and stare at it…After a while the roof jumps up, so that it now looks like two pages of an open book standing upright. Not only this, but the less brightly illuminated side now looks dirty grey, the other a brilliant white. If you now move your head from side to side, the “book” will appear to pivot around its center, turning wildly from side to side with your gaze.”
I’ve tried this, and after a few adjustments with the light, and remembering to keep one eye closed, it works very well and the resulting illusion is quite striking. In fact, there are many books and websites available showing interesting examples of stereographic optical illusions. Some use the effects of color contrasts or what Smith calls the “negative afterimage.” If you simply stare at a bright yellow piece of paper, the color will begin to fade; then, turning to a white piece of paper, you will see purple patterns interspersed with the white. Here, as in the other cases, the physical object is appearing to you other than it really is.
Another rather simple “do it at home” illusion is the “Ponzo” or “railroad tract” illusion. You draw two converging lines on a sheet of paper, like an upside down “V” (^). Then draw two horizontal lines between them, making sure they are exactly the same length. One parallel line is near the apex of the ^ and the other near the base. Then, regardless of the fact that you know the two horizontal lines are the same length, the top line will appear longer than the bottom line. Neuroscientists explain this by saying that the two converging lines “fool” the visual system into interpreting the two lines to be at some distance from each other. Even though the images of the horizontal lines are equal lengths on the retina, the visual system enlarges the line it sees as in the distance, in order to maintain what is called “size constancy.” Neuroscientists conclude from this that perception, in general, is “cognitively impenetrable.” Thus, our perceptual systems are immune to any intellectual correction, and work, in a sense, on autopilot, regardless of what we know in regard to the reality of the context.
Other popular stereographic visual anomalies are the famous “Neckar cube” and the “duck-rabbit” figure. In the former case, a drawing of a cube in one moment appears to be coming out towards you and in the next moment it appears to be receding. In the latter case, a figure appears to be a rabbit and switches to a duck. Scientists explain this as an “overload” of our optic system, which is unable to interpret two things simultaneously at the same place and time, so it switches back and forth from one interpretation to another. These examples seem to be ambiguous cases of illusion, since there is not one true reality of the way things “really” are. The so-called “laws of thought” ( A = A; either A or not-A; not both A and not-A) seem to have a physiological ground in the structure of our perceptual systems.
In general, perceptual illusion is more common than is realized. Although I have focused on visual illusions, every sense, including hearing, smell, taste, touch, as well as our perception of own bodily states, are subject to a wide variety of illusion. I will wait until my next article to discuss this further and glance at what it may imply in regard to the possibility of our direct access to world that exists independently of our perceptions of it. After all, the world presumably existed a long time before humans appeared on the scene, and changed everything.
Puzzle
On a circular clock, the hour and minute we at exactly equal distance from the six clock hour point. Then what time would it be, exactly?
Answer to last week’s puzzle
102564 was the pin number, since 4 x 102564 = 410256.
